In water treatment, silica is a problem because of its tendency to form deposits. It is often necessary to include reducing silica concentration to pen-nit increased cycles of concentration without scale. The behavior of aqueous silica and the various water treatment processes used for its removal were reviewed. Silica that exists in water in equilibrium with ion silicate can be removed by strong base anion-exchange resins operated in the hydroxide cycle. With the aim of silica removal by ion exchange, some thermodynamic and kinetic aspects were studied at different temperatures. Selectivity coefficients were determined and activity coefficients were calculated from an appropriate model. Silica concentrations were obtained by the measure of the absorbance of yellow or blue-colored silicomolybdic acid. Anion species concentrations were determined by ionic chromatography.